The Scottish Hebrides
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The Scottish Hebrides lie off Scotland's west coast. These islands have been inhabited since the Mesolithic period, 8,600 years ago and in many instances the origin of their names has literally been lost in the mists of time.
Lewis and Harris is the largest Scottish island and third largest in the British Isles. Its two names refer to two halves of the island. Lewis in the north is flatter and lower and Harris in the south varies from hilly to mountainous. Today 21,000 people live on the island including 8,000 in Stornoway. The island's economy was traditionally dominated by crofting and fishing but now tourism, fish-farming and renewable energy also contribute. Harris is the home of world famous Harris tweed. The island is virtually treeless with expansive areas of blanket peat bogs and exposed rock. It is home to nationally important breeding populations of waders, including redshank, dunlin, lapwing and ringed plover and provides habitat for corncrake, hen harrier, golden eagle and otter. |
Predator Eradication Project
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Island Size
Very large 2,179 sq.km |
Target Predators
American mink |
Eradication Methods
Kill trapping Initially live trapping |
Project Stage
Late stage eradication |
Visited
October 2018 |
Lewis and Harris Image Gallery
Click on an image to see a larger view with caption.
Read more about predator eradication on Lewis and Harris below.
Read more about predator eradication on Lewis and Harris below.
Eradicating American Mink
The Problem
American Mink were farmed for fur on the Outer Hebrides from the 1950's. Escapees inevitably established wild population's of mink on the islands and feral animals were recorded on Lewis by 1969. By 2001 they had spread as far south as South Uist having colonised Harris, North Uist and Benbecula along the way.
American Mink are a member of the mustelid family of mammals that also includes stoats, ferrets, weasels and badgers. They are carnivores and are skilled hunters, however, the only mustelid that naturally occurs on the Outer Hebrides is the European Otter. Otters principally eat fish and aquatic invertebrates whereas mink take more terrestrial prey in their diet including birds and mammals.
The introduction of American Mink to the Scottish Hebrides resulted in the loss of tern breeding colonies and increased nest predation of ground nesting waders, divers and waterfowl. Mink made it very difficult for crofters to keep domestic poultry including ducks and they also preyed on salmon in fish farms that support over 500 jobs on the islands. Therefore, the negative impacts of this introduced and invasive predator were not confined to ecological impacts but also had real economic and social impacts.
American Mink were farmed for fur on the Outer Hebrides from the 1950's. Escapees inevitably established wild population's of mink on the islands and feral animals were recorded on Lewis by 1969. By 2001 they had spread as far south as South Uist having colonised Harris, North Uist and Benbecula along the way.
American Mink are a member of the mustelid family of mammals that also includes stoats, ferrets, weasels and badgers. They are carnivores and are skilled hunters, however, the only mustelid that naturally occurs on the Outer Hebrides is the European Otter. Otters principally eat fish and aquatic invertebrates whereas mink take more terrestrial prey in their diet including birds and mammals.
The introduction of American Mink to the Scottish Hebrides resulted in the loss of tern breeding colonies and increased nest predation of ground nesting waders, divers and waterfowl. Mink made it very difficult for crofters to keep domestic poultry including ducks and they also preyed on salmon in fish farms that support over 500 jobs on the islands. Therefore, the negative impacts of this introduced and invasive predator were not confined to ecological impacts but also had real economic and social impacts.
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The Task
Between 2001 and 2006, American Mink were removed from the Uists. Trapping on Harris formed a buffer to prevent mink recolonising these islands. From 2006 to 2013 mink trapping focused on Lewis and Harris. A team of 12 full time professional trappers maintained a massive network of live traps across the island and checked them daily. As the mink population decreased, mink monitoring had to ramp up to ensure areas cleared of mink were not recolonised. Initially footprint recorders were used but now kill traps are used both to monitor the population and remove the last few animals remaining. |
The Outcome
In 2016 just seven mink were trapped on Lewis and Harris, including a non-breeding female. No juvenile animals have been caught since 2015. As a result of the near complete eradication of American Mink from Lewis and Harris, Scottish Natural Heritage report the number and distribution of tern colonies continues to grow and successful breeding is occurring in many small tern colonies. Indications are that birds such as divers, waterfowl and waders have also increased, crofters can again keep domestic poultry and mink impacts on farmed and wild fish stocks have been removed. |
Eradication Costs And Benefits
The Costs
Eradicating invasive predators is a costly exercise when measured in dollars and time. The eradication of American Mink on the Outer Hebrides is a salient example. Total costs approached £6 million, it took 17 years and 2,200 animals were trapped.
It is common to express costs in terms of a standard measurement. Viewed this way, each mink removed cost approximately £2,500. Alternatively the cost across the total control area, including the Uists, was approximately £1,800 per sq,km, or £18 per hectare.
These figures are large, but compared to other projects they suggest good value. In comparison, the rodent eradication on Lord Howe Island cost A$9.5 million, a similar amount of money, took around nine years to bring about, and is estimated to have killed 360,000 rats and mice on a 15 sq.km island. Costs per target animal were therefore about A$26, but costs per unit area were approximately A$6,500 per hectare.
A number of points emerge from this comparison:
Ultimately, the costs of eradicating invasive predators has to be weighed against the costs of not eradicating them. Choosing not to eradicate means having to accept reduced biodiversity and possibly even local extinctions of vulnerable populations of wildlife.
The Benefits
Rather than viewing eradication expenditure through a cost lens, viewing it through an investment lens brings eradication benefits into consideration. The question moves from "what will it cost" to "what will it return"?
In the case of mink eradication on the Outer Hebrides, important populations of arctic tern, common tern, little tern, black-throated diver, red-throated diver, corncrake, dunlin, ringed plover, eider duck, shelduck, teal and dippers were all under serious threat. However, because the direct benefits of securing these populations cannot easily be measured financially, evaluating an economic return on eradication investment is difficult. In contrast, direct economic benefits of ending damage to commercial productivity on fish farms is easier to see and measure.
Eradication expenditure also generates indirect benefits, such as skills and knowledge that can be applied elsewhere to reduce programme costs on later projects. In this respect, the Hebridean Mink Project is already benefiting the Orkney stoat eradication project. Other flow-on benefits of predator eradication come from tourism as visitors arrive to see for themselves what has been achieved.
Eradicating invasive predators is a costly exercise when measured in dollars and time. The eradication of American Mink on the Outer Hebrides is a salient example. Total costs approached £6 million, it took 17 years and 2,200 animals were trapped.
It is common to express costs in terms of a standard measurement. Viewed this way, each mink removed cost approximately £2,500. Alternatively the cost across the total control area, including the Uists, was approximately £1,800 per sq,km, or £18 per hectare.
These figures are large, but compared to other projects they suggest good value. In comparison, the rodent eradication on Lord Howe Island cost A$9.5 million, a similar amount of money, took around nine years to bring about, and is estimated to have killed 360,000 rats and mice on a 15 sq.km island. Costs per target animal were therefore about A$26, but costs per unit area were approximately A$6,500 per hectare.
A number of points emerge from this comparison:
- trapping invasive predators over extremely large areas can lead to a successful eradication if undertaken correctly
- for inhabited islands total programme costs using toxins may not automatically be a cheaper option than trapping
- considering costs alone only presents one side of the justification for attempting the eradication of an invasive predator
Ultimately, the costs of eradicating invasive predators has to be weighed against the costs of not eradicating them. Choosing not to eradicate means having to accept reduced biodiversity and possibly even local extinctions of vulnerable populations of wildlife.
The Benefits
Rather than viewing eradication expenditure through a cost lens, viewing it through an investment lens brings eradication benefits into consideration. The question moves from "what will it cost" to "what will it return"?
In the case of mink eradication on the Outer Hebrides, important populations of arctic tern, common tern, little tern, black-throated diver, red-throated diver, corncrake, dunlin, ringed plover, eider duck, shelduck, teal and dippers were all under serious threat. However, because the direct benefits of securing these populations cannot easily be measured financially, evaluating an economic return on eradication investment is difficult. In contrast, direct economic benefits of ending damage to commercial productivity on fish farms is easier to see and measure.
Eradication expenditure also generates indirect benefits, such as skills and knowledge that can be applied elsewhere to reduce programme costs on later projects. In this respect, the Hebridean Mink Project is already benefiting the Orkney stoat eradication project. Other flow-on benefits of predator eradication come from tourism as visitors arrive to see for themselves what has been achieved.
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